| The carbon transformation and change of humus during composting with different raw materials were studied under aerobic composting condition. Two kinds of excrements of livestocks, cow dung, and sheep dung were combined with two types of straws, maize and wheat, as treatments.The four treatments includes: T1—cow dung+maize straw; T2—cow dung + wheat straw; T3—sheep dung + maize straw; T4—sheep dung + wheat straw. The results showed that the content of total organic carbon (TOC)of all treatments decreased throughout the composting process.The TOC content of T1 to T4 decreased by 22.1%, 21.5%, 23.6% and 23.7%, respectively. The changes in dissolved organic carbon(DOC)were consistent with TOC, and dropped to the minimum at day 15 as 6.57,5.47,4.73 g·kg-1 and 4.93 g·kg-1, respectively,but showed the different characteristics. T1 and T2 treatments of cow dung composters showed no changes until day 10 but the DOC of T3 and T4 treatments with sheep dung composts decreased at the beginning of the composting. By the 15th day of composting, the decreases of T1~T4 treatments were 32.4%,36.5%,51.8% and 39.3%, respectively. The total humicacid(THA)in composting started increasing at day 10 and continued increasing until reached maximum at day 15. The THA in T1-T4 increased to 25.5%, 22.5%, 29.8%, and 30.0%, respectively. The THA of T3 and T4 treatments were significantly higher than that of T1 and T2 (P＜0.05). As the composting process progressed, the content of free humic acid (FHA) gradually decreased, and decreased by 7.6%~18.0% at the end of composting. The content of HA gradually increased, and increased by 65.4%~197.8% at the end of composting. The percentage carbon in HA increased during the composting process. The contents of FHA and HA in T3 and T4 treatments were higher than those in T1 and T2 treatments throughout the composting process. FA content decreased gradually with the composting process, and decreased by 44.9%~54.9% at the end of composting. The high content of cellulose and hemicellulose in sheep dung may contributed to the high content of free humic acid in composting process. It may suggest that more sheep dung should be added to increase the percentage carbon in HA forms and improve the quality of compost products. |